Service providers set up roaming agreements with other service providers in different geographic regions so that when the user is in a region where the home service provider does not offer a service, nevertheless the service can be provided by a different service provider who has a billing arrangement with the home service provider. Any particular region may support different systems and networks. For CDMA (Code Division Multiplex Access) networks, a Preferred Roaming List PRL which is stored at the mobile device provides information about which system/network is preferred in the region for that device. Over-the-air (OTA) Management protocols allow data to be transmitted to mobile devices via wireless transmission media. One example of OTA Device Management is the re-programming of the Preferred Roaming List (PRL). When a mobile user is abroad and switches on the mobile device for the first time, the mobile device performs a search for all available networks. The mobile device then reads from the PRL the preferred networks and the order in which they should be offered to the user. Since preferred networks are constantly changing as new roaming agreements are made, it is necessary to frequently update the PRL in the mobile device. This is achieved by downloading the revised PRL remotely using OTA technology. OTA protocols are defined for example in the over-the-air service provisioning/parameter administration (OTASP/OTAPA) and Open Mobile Alliance (OMA) device management standards.
Current protocols developed in OMA (Open Mobile Alliance) DM (Device Management) provide an integrated framework for OTA management of 3G mobile devices. The existing OMA DM protocol defines a management framework and a set of messages exchanged between one mobile device and an entity in the network called the management server. A management session is set up between the management server and the mobile device, and an OTA message is constructed which is unique to the mobile device.
FIG. 1 illustrates the structure of a preferred roaming list PRL for CDMA networks. There is a system table ST1 . . . STi . . . STn associated with each geographical region which contains a list of system descriptions keyed by system identifier/network identifier (SIN/NID) pairs and associated with an acquisition index. The acquisition index is used as a pointer to an acquisition table AT which contains an indexed list of RF channels for channel acquisition purposes in the new network.
According to the current standard, system acquisition can be carried out using frequency blocks with Personal Communication Systems (PCS) assigned values, or by using channel numbers with the highest priority channel first.
To date preferred roaming lists are provided only in the context of CDMA operation, which includes system selection in analogue mode and CDMA mode.
Currently, for GSM mobile equipment, a list of preferred Public Land Mobile Networks (PLMNs) is stored in the Subscriber Identity Module (SIM) of the mobile device. This enables roaming through PLMN selection when the mobile equipment is outside the home network. However, a GSM mobile device would have no information about a CDMA network in its geographical region or vice-versa.
So-called multimode devices are currently being developed which should be capable of roaming in heterogeneous network environments. For example, a device originally provisioned in a CDMA network should be capable of roaming in a GSM, WLAN (Wide Local Area Network), UMTS (Universal Mobile Telecommunications Systems) or any other network.